A discharge line for exhaust gas from equipment, such as, for example, a coal-fired boiler or the like, in which coal is burnt is provided with an exhaust gas treatment catalyst for treating nitrogen oxide (NOx) in the exhaust gas. The exhaust gas treatment catalyst is obtained by the following process: titanium oxide (TiO2) as a main component, and further tungsten oxide (WO3), vanadium oxide (V2O5), and the like are kneaded together with a binder, molded into a honeycomb shape so as to have multiple holes, and calcined. A reducing agent such as ammonia (NH3) is flowed into the holes together with the exhaust gas to bring the nitrogen oxide in the exhaust gas and the reducing agent into contact with the wall surfaces of the holes. This enables the decomposition and removal of the nitrogen oxide.
While such an exhaust gas treatment catalyst is being used, ash (fly ash) generated by burning coal is continuously flowed into the holes together with exhaust gas. Thus, components such as calcium (Ca) in the fly ash gradually adhere (to a thickness of several tens μm) on the inner wall surfaces of the holes. Such components inhibit the contact reaction between the nitrogen oxide and the reducing agent on the catalyst surface. Additionally, the fly ash itself is partially deposited inside the holes, and gradually makes it hard for exhaust gas to flow into the holes. Eventually, the fly ash completely blocks and clogs the holes, accordingly lowering the denitration performance.
Against this background, the exhaust gas treatment catalyst used for a predetermined period is regenerated as described in, for example, Patent Document 1. Specifically, an exhaust gas treatment catalyst is crushed such that 70 to 95 wt % of the whole exhaust gas treatment catalyst becomes coarse pieces having a size exceeding a threshold size S (any value in a range of 0.105 mm to 1.0 mm) (crushing step). Fragments thus obtained by crushing the exhaust gas treatment catalyst are separated into the coarse pieces having a size exceeding the threshold size S and fine particles having a size not larger than the threshold size S (separating step). The separated coarse pieces are pulverized into such a fine powder that has an average particle diameter not larger than 0.1 mm (pulverizing step). The fine powder is kneaded together with other raw materials and molded into an exhaust gas treatment catalyst (kneading step and molding step). The molded precursor is dried and calcined (around 500° C.) (drying step and calcining step). Thus, a regenerated exhaust gas treatment catalyst is obtained.